she said to Abraham
"Sarah said to Abraham"
"send away" or "get rid of"
this slave woman and her son
This refers to Hagar and Ishmael. Sarah probably did not refer to them by name because she was angry with them.
with my son, with Isaac
"with my son Isaac"
This thing was very grievous to Abraham
"Abraham was very unhappy about what Sarah said"
because of his son
"because it was about his son." It is implied that this means his son, Ishmael. (See: rc://en/ta/man/translate/figs-explicit)